Coloring anodized aluminum



Dec. 24, 1968 w. A. FAHLBUSCH COLORING ANQDIZED ALUIINUI Fina llarch 29.1966 SURFACE PRETR'E'ATMENT uomzms LOW TEMPERATURE DRY! N6 mmicuxrmcSURFACE CLEANING AND. SEAL! N 6 IN VEN TOR.

. WILLIAM A. FAHLBUSCH United States Patent Ofi 3,418 ,2 l 9 PatentedDec. 24, 1 968 ice 3,418,219 COLORING ANODIZED ALUMINUM lVilliam A.Fahlbusch, Arlington Heights, Ill., assiguor to Martin-MariettaCorporation, New York, N.Y., a corporation of Maryland Filed Mar. 29,1966, Ser. No. 538,389 12 Claims. (Cl. 204-38) The present invention isrelated to the coloring of anodized aluminum and, more particularly, tothe production of a black color on anodized aluminum.

In the past there have been proposed a number of processes for producingcolored anodized metal, especially black colored aluminum. Theseprocesses are generally of two kinds. First a color may be introducedinto the pores of an anodic film on the surface of anodized aluminum bythe use of one or more colored dyes carried in either an aqueous bath oran organic vehicle. The second type of process involves the formation ofa colored precipitate in the pores of the anodic film. Such a coloredprecipitate is often a metallic sulfide and, more particularly, isproduced by a metathetical reaction wherein a metal ion is absorbed intothe anodic pores followed by the subsequent absorption of sulfide iontherein.

The aforementioned prior art processes have certain disadvantages. Withvery few exceptions, organic colorations are subject to fading throughthe action of light, oxidation and the like. With respect to the priorart metallic sulfide colors, it is very difficult to obtain uniformcoloration in any reasonable length of time. Since the depth of color isdependent upon the relative completeness of diffusion, time, oftenamounting to up to about one hour, must be allowed to permit diffusionto occur. The fact that a solid product, i.e., the sulfide precipitate,is forming in narrow pores in the anodized layer during diffusion slowsdown the rate at which the color develops. In view thereof it isdifficult to achieve a uniform, deeply colored aluminum by the usualmetathetical reactions proposed heretofore. As far as is known, the arthas not been provided with a commercially acceptable process whereby thedisadvantages enumerated hereinbefore can be overcome.

It has now been discovered that by means of a novel combination ofingredients employed in a novel manner deep, commercially satisfactory,black colorations can be produced in anodized metal.

It is an object of the present invention to provide a novel process forthe production of black-colored anodized metal.

Another object of the present invention is to provide a novelcomposition of matter useful in the formation of black-colored anodizedaluminum.

A further object of the present invention is the provision of novelcoloring solutions for use in the coloration of anodized aluminum.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the drawing in which the figureshows a schematic outline of an anodizing and coloring process involvinguse of the present invention.

Generally speaking, the present invention contemplates a coloringprocess wherein a porous anodized surface is impregnated with an aqueoussolution containing in solution a substance capable of donating aprecipitant ion (e.g., sulfide ion) at temperatures in excess of about200 F. and stable in aqueous solution at temperatures below about 100 F.and an ion capable of reacting with the precipitant ion to form acolored precipitate which is insoluble in water and heating the thusimpregnated anodized surface to a temperature in excess of about 250 F.for at least about one or two minutes whereby the anodized surface iscolored. Heating times can be up to any practical length of time and areprincipally dependent upon temperature. Longer times are employed atlower temperatures and shorter times are employed with highertemperatures.

The present invention further contemplates as a composition of matter acoloring impregnant for coloring anodized metal comprising an aqueoussolution containing in solution metalliferous ion capable of reactingwith the sulfide ion to form a colored sulfide which is insoluble inwater, at least an amount of a substance capable of donating sulfide ionat temperatures in excess of about 200 F. and stable in aqueous solutionat temperatures below about F. effective to provide sutficient sulfideion under reaction conditions to react with said metalliferous ion, athickening agent in an amount effective to induce in the aqueoussolution a workable viscosity for the means by which the coloringimpregnant is applied to the anodized metal and a stabilizing agent. Inaddition, the aqueous solution can contain dispersed therein aninsoluble substance designated in this specification and claims as aflattening agent.

The ion capable of reacting with the precipitant sulfide ion used in thecoloring process of the present invention is at least one member of thegroup consisting of the ions of cobalt, copper, antimony, nickel,molybdenum, iron, and bismuth. In order to obtain a stable blackcoloration in the anodized surface, it is advantageous to employ ions ofcobalt, nickel or iron. It is pertinent to note that the ion employed insolution can be not only a simple hydrated ion of a metal mentionedhereinbefore but also a complex ion which contains as a part thereof ametal mentioned hereinbefore. When a complex ion is employed, it isnecessary that the complex ion be capable of thermal degradation at atemperature below about the heating temperature. The use of the termprecipitant ion in this specification and claims is not intended toimply that color formation is a precipitation in the usual sense. Thesubstance causing the color in the final product is usually awater-insoluble substance but is not necessarily produced in thepresence of water.

The substance capable of donating sulfide ion at temperatures in excessof about 200 F. and stable in aqueous solution at temperatures belowabout 100 F. (hereinafter called sulfide doner) is advantageously sodiumthiosulfate. The sulfide donor is generally a sulfur-containingsubstance capable of dissolving in water in an amount to provide atleast about 0.1% of sulfur available for reaction. Operable sulfidedonors include ammonium thiosulfate, potassium thiosulfate, thiourea(thiocarbamide), and substituted thioureas in addition to sodiumthiosulfate.

Thickening agents operable in the present invention include a colloidalsuspension of boehmite-type aluminum oxide known in the trade as Baymal,soluble starches such as arrowroot starch, hydroxy alkyl celluloses(e.g. hydroxyethyl cellulose), polyvinyl alcohol, polyacrylamide, methylvinyl ether copolymer with maleic anhydride sold under the trade nameGantrey AN, polyvinylpyrrolidone and an ethylene oxide polymer such assold under the trade name Polyox WSR Resin. Such thickening agents areemployed in amounts of about 0.1 and up to about 20 or even 50 or moreparts by weight of thickening agent per 100 parts by weight of water.Because of ionic efiects on the viscosity of a colloidal suspension, itis impossible to specify with accuracy the exact amount of thickeningagent needed to achieve the required viscosity without specifying thecharacter and amount of each ionic species present in impregnatingcomposition of the present invention. It will be found, however, that anamount of thickening agent in the range of parts by weight, as specifiedhereinbefore, will usually suflice to achieve the required viscosity.

The use of a stabilizing agent in the coloring solutions of the presentinvention which contain sodium thiosulfate is highly advantageous and insome instances essential if one is to be assured that the coloring bathis to be stable for even short periods of time. It is possible forunstabilized solutions to exist for a measurable period of .time withoutthe appearance of precipitated sulfide. Such solutions can be used, forexample, by being mixed in a spraying device immediately prior to sprayapplication. In some instances where a bath life in excess of about 15minutes or a half hour is not necessary, unstabilized baths may be usedfor dip, roller or other types of coating. In the usual case, however,it is highly advantageous to employ at least about 0.1% by weight ofsodium or potassium bisulfite in the bath as a stabilizing agent. It iseven more advantageous to employ at least about 0.3% of such stabilizingagent in the bath. Normally no more than about 1% of stabilizing agentis necessary but up to about 5% by weight or more can be used ifdesired. In the case of sodium thiosulfate solutions containing thecuprous ion as the sole coloring ion, the presence of at least about0.3% by weight of stabilizing agent is a practical necesssity since suchsolutions often can deteriorate by precipitation in very short spaces oftime. Except for molybdenum solutions, all the sodium thiosulfatesolutions of the present invention appear to be stable at the pHproduced by the ingredients, which pHs are normally slightly acidic(i.e., a pH of 4 to 6). The pH of molybdenum-containing solutions mustbe adjusted to at least as high as about 7. Impregnating (coloring)compositions or solutions of the present invention containing thioureaappear to be shelf stable at least for several months without anystabilizing addition.

Optionally, but nevertheless highly advantageously, one can employ up toabout 50% by weight or more (based on weight of solution but notincluded therein) of a flattening agent. A flattening agent for purposesof this specification and claims is a finely divided, essentially insertsubstance such as titanium dioxide (pigment grade), rouge (iron oxide),finely ground mica, finely divided chemically stabilized clay or thelike. For dipping or sprayin purposes, the use of a flattening agent inan amount within the aforestated range and more particularly withinabout 5% to 20% by weight dispersed in the coloring solution is highlyadvantageous. The flattening agent enhances evenness of coverage of themetal to be colored and, in general, improves the workability of thecoloring compositions.

As is obvious to one skilled in the art, the impregnating compositionwill contain addition ions balancing the colorproducing ion instoichiometrically equivalent amounts to permit electronic balance inthe aqueous solution of the impregnating composition. Thesecomplementing ions necessarily are such that, together with themetal-bearing ion, they will produce a water soluble material stable inaqueous solution. Where mixtures of metallic species are employed, it isnecessary to avoid mutually incompatible ions. For instance, one couldnot employe cobalt sulfate and lead acetate together in the same aqueoussolution since metathmis dictates in this case the formation of leadsulfate an undesirable, substantially water-insoluble material. In likemanner, salts, such as cobalt chloride and silver sulphate, are alsomutually incompatible in an aqueous solution.

The base metal which is colored by means of the present invention isusually aluminum (including for purposes of this specification andclaims anodizable alloys containing more than about 80% aluminum) butcan be another anodizable metal such as titanium. In preparing aluminumfor the coloring process of the present invention, it is usuallynecessary to anodize in such fashion as to produce a surface anodic filmat least about 0.1 mil thick. For architectural purposes it isadvantageous that the anodic film be at least about 0.5 mil thick, forexample about 0.7 mil or thicker. Those skilled in the art willrecognize that such anodic films may be produced in a number ofdifferent ways. In order to describe the invention with the utmost TABLEI Broad aspect Preferred aspect Type of electrolyte H2804 H2804.Concentration of electrolyte. 4 to 30% by weight- 15% by weight.

Anodic C.D 21:0 100 a111ps./it. 10 amps/ftfl. Time 0.5 to minutes" 40minutes. Temperature 25 to F 72 F.

* Ampslftfi=amperes per square foot.

It is to be noted that while preferred conditions of anodizing have beenset forth in Table I under the heading Preferred Aspect, these preferredconditions are, in truth, designed to provide a satisfactory anodizedcoating about 0.7 mil thick on an aluminum alloy known to the art asgrade 6063 containing nominally in percent by weight about 0.45 to 0.90%magnesium, about 0.2 to 0.6% silicon, not more than 0.35% iron, 0.1%each of copper, manganese, chromium, zinc [and titanium in addition toaluminum. As .those skilled in the art will recognize, each aluminumalloy will require subtle adjustments of the anodizing conditions withinthe broad range set forth in Table I to produce an equivalent coating.Since it may be possible to produce equivalent coatings in anon-electrolytic manner, the term anodizing is used in thisspecification and claims to include any and all means of forming aporous, adherent surf-ace coating at least about 0.1 mil thick, whichcoating is substantially equivalent to those coatings produced under thebroad conditions set forth in Table I.

Once the anodizing has been completed, the anodized object is rinsed andallowed to dry at about room temperature. The thickened solution of thecoloring impregnant of the present invention is then applied to theanodized surface. While the thickened solution can be applied in anyfashion which will produce an evenly distributed wet coating, it hasbeen found to be advantageous to spray the thickened solution ontosubstantially horizontally oriented surfaces. It is possible and may attimes be advantageous to arrange matters such that thickening of thesolution occurs immediately prior to or simultaneously with thespraying. In this manner it is possible to employ thickening agentswhich, after a time, will become unstable in the presence of ionicsolutions. After the freshly anodized surface has been sprayed with thethickened solution, it is immediately heated to a temperature of about250 F. to about 1100 F. for about 2 to about 60 minutes. Generally it isadvantageous to heat within the range of about 300 F. to about 600 F.with the greatest amount of control and flexibility being obtained whenheating is conducted within the range of 350 F. to 450 F. It has beenfound satisfactory to heat to a temperature of about 400 F. for about 15minutes. The heating can be accomplished by using an oven, by inductionheating or by any other heating means known to the art, which heatingmeans will not disturb the treated surface of the anodized metal. Infurther explanation of the heating operation, it is to be understoodthat when it is stated that a treated surface is heated to a temperatureof about 400 F. for 15 minutes, this procedure is carried out when awet, treated sheet metal object is introduced into an oven having anambient temperature maintained within plus or minus 10 in Fahrenheitunits of 400 F. It is recognized that attainment of the oven temperatureby an object introduced therein is subject to a lag, especially when thesurface of the object is wetted with an aqeuous solution. Further, it isrecognized that the mass of an object introduced into an oven is adetermining factor as to the speed with which the object attains oventemperature. Accordingly, for purposes of this specification,temperatures and times are given with the understanding that sheet metalobjects are being treated and that the oven or other heating means is ofa suflicient capacity to heat a sheet metal object without losingtemperature to any substantial degree. As

those skilled in the art will readily recognize, modifications of thetime and/or temperature ranges may have to be made if conditions orsituations other than those specifically described herein areencountered. After heating, anodized and colored aluminum is usuallyfound to be sealed as shown by the ASTM Dye Test Designation B-13663TResistance of Anodically Coated Aluminum to Staining by Dyes. In someinstances, such as when treating 1100 alloy, only partial sealing isattained.

For further corrosion protection the anodized and colored aluminum canbe treated with polar aliphatic compounds, lacquers, Waxes, boilingwater, heated aqueous metal salt baths such as sodium dichromate, nickelacetate, etc. Treating with boiling water gives a velvety appearance toa black colored aluminum which at times may be desirable.

In carrying the present invention into practice, the concentration ofthe various reactants (color forming metal salt and precipitant) andcontrol agents may vary widely. For example, the color forming salt maybe used from a 1% concentration up to saturation, about 515% beingusually advantageous. The sulfide donor can be used from a 1%concentration up to saturation, about 15 to 30% being usual. Thesolution stabilizing agent can be used from a 0.1% concentration up toabout 3%, e.g. about 0.75 to about 1.25%. The flattening agent can beused from a 1% concentration up to 50% or more. About 2- 8% offlattening agent is usually sufficient. The thickening agentconcentration is governed by the ionic effects on the viscosity of acolloidal suspension. Thus, the thickening agent can sometimes bepresent in minute amounts or can be present up to concentrations thatwill form very viscous solutions. A particularly advantageous range forBaymal alumina is about 1 to 10%, e.g. 24%.

In carrying the present invention into practice, it is advantageous toemploy as a blackening impregnant an aqueous composition made up withthe following:

Substance: Amount in percent by weight Cobalt chloride hexahydnate 4 toSodium thiosulfate pentahydr'ate 12 to Sodium bisulfite 0.5 to 1.25Rouge (Pe O 2 to 8 Baymal 1 to 4 Water Balance Blackening isaccomplished by impregnating an anodized aluminum surface with thecobalt-containing ingredient and thereafter heating for about 15 minutesin an oven maintained at 400 F.

For the purpose of giving those skilled in the art a better appreciationof the advantages of the invention, the fol lowing specific examples aregiven:

EXAMPLE I A sheet of aluminum alloy designated as grade 6063 andcontaining in addition to aluminum about .45.90% of Na S O .5H O 250NaHSO l0 CoCl .6H O 100 To 700 ml. deionized water add the :aboveingredients and when dissolved dilute to 1 liter with water.

Solution for spraying In a high speed blender, blend 300 ml. of mastersolution 20 gm. rouge (Fe O 100 ml. 10% Baymal in water EXAMPLE IIAluminum alloy 6063 is anodized as in Example I. A sample of theanodized alloy is impregnated by immersing in coloring solution andWithdrawn at the rate of about 3" per minute. Solution composition is asfollows:

Gm. CoCl .6H O 100 (NH CS (thiourea) 100 Arrowroot starch 3% to 1 liter.

Dissolve the above salts in approximately 700 ml. of 3% aqueous solutionof arrowroot starch. When dissolved dilute to 1 liter with the starch.

Aluminum sheet after impregnation heated as in EX- ample 1.

EXAMPLE III A buffed sheet of aluminum alloy designated as grade 5457and containing in addition to aluminum about .80 1.20% magnesium, about.15.45% manganese and about .20% copper, .10% iron and .08% silicon wasanodized in a 15 H 50 water bath :at 72 F. for about minutes to producean anodic film about 0.5 mil thick. The anodized alloy divided into twoparts was then dried in air at room temperature, treated as in ExamplesI and II and heated to 400 F. for 15 minutes. Excess salts Were removedby washing with water. A bright jet black color was obtained.

EXAMPLE IV Aluminum alloy 6063, anodized as in Example I, was sprayedwith an impregnating composition prepared as follows:

Master solution Grams NEI S OySI-I O 250 NaHSO 10 CuCl Dissolve the Na SO -5H O and NaHSO in approximately 700 ml. of H 0. When dissolved addthe CuCl and when dissolved dilute to 1 liter.

Solution for spraying In a high speed blender, blend 300 ml. mastersolution 20 gm. rouge (Fe O 200 ml. 10% Baymal After heating andcleaning, as described in Example I, a dark green color was obtained inthe anodized layer.

EXAMPLE V Aluminum alloy 6063, anodized as in Example I, was sprayedwith an impregnating composition prepared as follows:

Master solution Grams Na S O -5H O NaI-ISO 10 CdCl -2 /z H O Dissolvethe above salts in approximately 700 ml. deionized H O. When dissolveddilute to 1 liter with H O.

Solution for spraying In a high speed blender, blend 400 ml. mastersolution 20 gm. rouge (Fe O 150 ml. 10% Baymal After heating andcleaning, as described in Example I, a bright canary yellow color wasobtained in the anodized layer.

EXAMPLE VI Aluminum alloy 6063 is anodized as in Example I. The anodizedalloy was then sprayed with an impregnating composition prepared asfollows:

Master solution Grams Nagsgog NaHSO 10 CuCl 25 MOqOgg Dissolve the firsttwo salts in approximately 700 ml. deionized water. When dissolved,dissolve the third and then the fourth salt. When dissolved immediately,adjust pH to 7.0 with NH OH and dilute to 1 liter with H O.

Solution for spraying In a high speed blender, blend 350 ml. mastersolution 20 gm. rouge (Fe O 100 ml. 10% Baymal After heating andcleaning, as described in Example I, a red-brown color was obtained inthe anodized layer.

Additional examples of anodized alloys treated in accordance with thepresent invention are set forth in the following table together with thecolors produced.

Colored anodized metal, e.g. aluminum, produced in accordance with thepresent invention, is particularly adapted for architectural uses on theexterior of buildings and in any other locations Where exposure tosunlight exists. The colors produced are resistant to fading in sunlightand are resistant to the detrimental action many substances carried innormal urban atmospheres. Many other uses can be contemplated foraluminum colored in accordance with the present invention. For example,attractive eifects can be produced by combining the coloring procedureof the present invention with other metal treatments such aspre-anodizing, texturing, partial masking of surfaces duringimpregnation of the coloring solutions of the present invention and thelike, which effects can be employed wherever decorated metal isrequired. Above and beyond mere decoration, the process of the presentinvention can be employed to provide surfaces which absorb or radiatemoderate amounts of heat and thus provide utilitarian as well asaesthetic effects.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand.

Such modifications and variations are considered to be within thepurview and scope of the invention and appended claims.

I claim:

1. A process for producing a color on anodized metal comprisingimpregnating a porous anodized layer on said metal with a stable,aqueous solution containing both a precipitant ion donor and an ion,said solution being unstable at an elevated temperature of a metalcapable of forming a colored precipitate with said precipitant ion andsubsequently heating the thus impregnated anodized layer at atemperautre effective to induce formation of said colored precipitate.

2. A process as in claim 1 wherein the precipitant ion is sulfide ion.

3. A process as in claim 2 wherein the sulfide donor is a substanceselected from the group consisting of sodium thiosulfate, potassiumthiosulfate, ammonium thiosulfate, thiourea and substituted thioureas.

4. A process as in claim 2 wherein the sulfide donor is sodiumthiosulfate and the metal capable of forming a colored sulfide isselected from the iron group metals.

5. A process for producing a color on anodized metal comprisingimpregnating a porous anodized layer on said metal with a stable aqueoussolution containing a metalliferous ion from the group of cobalt,copper, antimony, nickel, molybdenum, iron, and bismuth ions, sodiumthiosulfate and at least about 0.1% by weight of sodium bisulfite and,thereafter, heating the thus impregnated porous anodized layer at atemperature in excess of about 250 F. for at least about one minute.

6. A process as in claim 5 wherein the sodium bisulfite is present in atleast about 0.3% by weight.

7. A process as in claim 5 wherein the metalliferous ion is an ion ofthe iron group metals.

8. A process as in claim 5 wherein the heating is conducted for about 15minutes at a temperature of about 400 F.

9. A process as in claim 5 wherein the stable aqueous solution has aflattening agent dispersed therethrough.

10. As a composition of matter an aqueous solution containing dissolvedtherein at least one metal bearing ion bearing a metal from the groupconsisting of cobalt, copper, antimony, nickel, molybdenum, iron, andbismuth, a sulfide donor from the group consisting of sodiumthiosulfate, potassium thiosulfate, ammonium thiosulfate, thiourea andsubstituted thioureas, a thickening agent and, at least when copper isthe sole metal bearing ion and when a thiosulfate is the sulfide donor,an effective amount 1 of sodium bisulfite up to about 5% by weight tostabilize said solution.

11. A composition of matter as in claim 10 wherein the solution also hasdispersed therethrough up to about 50% by weight of a flattening agent.

12. A composition of matter as in claim 10 wherein the sulfide donor issodium thiosulfate and the metal is an iron group metal.

References Cited UNITED STATES PATENTS 2,018,388 10/1935 Tosterod 204-353,152,970 10/1964 Jensen 204-35 JOHN H. MACK, Primary Examiner.

R. L. ANDREWS, Assistant Examiner.

US. Cl. X.R.

1. A PROCESS FOR PRODUCING A COLOR ON ANODIZED METAL COMPRISINGIMPREGNATING A POROUS ANODIZED LAYER ON SAID METAL WITH A STABLE,AQUEOUS SOLUTION CONTAINING BOTH A PRECIPITANT ION DONOR AND AN ION,SAID SOLUTION BEING UNSTABLE AT AN ELEVATED TEMPERATURE OF A METALCAPABLE OF FORMING A COLORED PRECIPITATE WITH SAID PRECIPITANT ION ANDSUBSEQUENTLY HEATING THE THUS IMPREGNATED ANODIZED LAYER AT ATEMPERATURE EFFECTIVE TO INDUCE FORMATION OF SAID COLORED PRECIPITATE.